1. Field of The Invention
This invention relates to a biasing coil used in multi-stage surge suppression and transient protection. More particularly, it relates to a non-ferrous biasing coil used in surge suppression and transient protection of electronic devices and data communication lines wherein multiple coils are employed in close proximity to one another, positioned at angles, and dual-wound.
2. Background of the Prior Art
Inductive-capacitive filter biasing coils used for the purpose of surge protection and surge suppression systems are known in the prior art. FIG. 3 of the drawings illustrates that a pair of biasing coils having a ferrous material core inserted within a center portion of each coil are used to offer surge protection to electronic devices and data communication lines. However, these coils are not dual wound; in fact they are separated by a measurable space, typically mounted on a circuit board (to be discussed in more detail hereinafter).
Other surge elements such as metal oxide varistors (MOV), avalanche diodes (SAD) and gas tube devices have been used for years to divert surge voltages and currents in a power or data communication line to ground as a method of protecting against surges. Surge elements, as used herein, are defined as devices that divert voltage and current surges.
Surge elements are typically connected in shunt configuration between two conductors in a power or data communication line circuit. The surge elements are therefore inert during normal circuit conditions (normal operating conditions) but conduct at low impedance during a surge voltage condition or other like transient anomaly.
Prior art surge elements are constructed in limited configurations and have limited surge handling capabilities. It is not uncommon in the prior art to provide parallel multiple stage surge devices to increase current conductive capabilities. Unfortunately, due to differences in the individual surge elements, it is difficult to bias the current through the multiple stage surge elements. In fact, it is quite typical that the surge current is unequal throughout the multiple surge elements thereby causing an insignificant improvement in current handling as that compared to individual surge elements capable of handling the surge or transient on its own.
Some prior art surge suppression devices insert a series inductive coil or resistor between multiple parallel connected surge elements. This type of circuit forces each surge element to share the available surge current. This current sharing reduces the circuit impedance under surge conditions thereby permitting a lower surge voltage to reach the protected electrical equipment or data communication lines downstream from the surge suppressor.
However, the aforementioned prior art devices have many inherent disadvantages which are not easily overcome. Some surge suppression devices are known to allow normal electrical voltages and currents to pass there through without reacting. However, some devices, employing series coils or resistors, conduct normal line current but experience heating during normal line current carrying conditions. This is undesirable. Series type devices must therefore be designed to limit the normal circuit current. However, this is also undesirable. To overcome these inherent problems of the prior art, very large coils can be employed in some surge suppression devices so that normal current conditions can be conducted. However, the use of very large coils can be expensive and be a waste of valuable, limited space; again achieving an undesirable result.
An attempt to improve the large coil problem involves winding much smaller coils around a ferrous material core (see FIG. 3), thereby reducing the number of turns needed for the coil. Ferrous materials are typically used since they have a high permeability and a small conductivity. Unfortunately, in AC electrical systems, the ferrous coil reacts to the changes in current, thereby creating unwanted heat as in the large coil configurations. This results in the ferrous coil limiting current passing through the circuit as well as limiting the actual size of the coil that can be used.
Unwanted heat and the actual overheating of the coils is a big problem in the protection of electronic circuits from overvoltages and surge currents. In some instances, U.L. temperature ratings are exceeded, causing the suppression device to be re-designed to comply with U.L. requirements. This of course can cause insufficient suppression capability for a particular surge suppression device, at the expense of U.L. compliance. This in turn translates into the possibility of a damaging surge or transient reaching the electrical equipment or data communication line that is positioned downstream from the suppression device.
Further, large surge currents can cause intense magnetic fields inside the ferrous cores and are known to saturate the core during these surges. This decreases the inductance; in fact, the inductance of the ferrous core coil can completely vanish if the core becomes completely saturated by an intense magnetic field.
Even though the ferrous core coil configuration is an improvement over the larger coil style alone, it still represents a limitation in the prior art which needs to be improved upon. It is also noted that series coil systems, due to coil size and their method of manufacture (i.e., ferrous core configurations) are expensive to build.
A further inherent disadvantage in series coil systems is that the ferrous cores store energy that reacts with the incoming surge current or like transient anomaly. Also, when series coils are combined with surge elements in a parallel configuration, they react to the switching of the surge elements and create a high frequency “ringing” surge voltage. This too is undesirable. These ringing high frequencies are not addressed by the prior art surge suppressors even though they can be extremely damaging to equipment downstream from the original surge voltage.
Another surge protection device that utilizes coils known in the prior art is a “common-mode choke”. These devices insert large inductance in series on a common-mode line source (signals in which have identical amplitude and phases at both inputs). Common-mode chokes have two independent coils of the same size and the same number of turns. Typically they are wound on a toroidal-shaped ferrous core. However, many of the inherent problems that exist in the other ferrous core coils also exist here. Therefore common-mode chokes are considered inadequate for today's surge suppression and transient protection needs.
An improved surge suppression device is clearly needed that overcomes the inherent deficiencies in the prior art. Such improved device should not rely upon ferrous core style coils or very large air-core style coils. The improved surge suppression device should not limit the normal line current, yet it should adequately protect downstream electrical and data equipment by suppressing voltage and current surges and other like damaging transient anomalies. Further, overheating of the coils should be avoided to comply with U.L. requirements. In other words, coils cannot exceed temperature ratings when carrying circuit load current. For example, a series device plugged into a standard wall receptacle is tested to a full 15 amp load carrying capability and nothing within the device can exceed the temperature ratings for such a load. A typical problem with ferrous core coils is that they will reach temperature that will result in melting of the plastic cases, hence they will not pass normal load current tests.